The Ohio State University College of Mathematical & Physical Sciences Department of Astronomy

Optical Design

Paul Byard has worked with Brooke Gregory (CTIO) to translate the optical design prescriptions from Code-V to OSLO, and they agree they both have the same design in their respective programs. Brooke has agreed to do a thorough review of the optical design before we send the optics package out for bid. He and Paul are now discussing how to best quantify the image analysis. It is clear we need more than just one number (e.g., the "error function"), and are looking at comparing predictions of D₈₀ (80% encircled energy diameters). We discussed how we might make D₈₀ contours and other ways to visualize the imaging performance in meaningful ways.

Brooke will be coming to Ohio State the first week of April to go over the optical design with us in detail. The goal is still to have the optical bid packages ready around April 15.

Paul will be presenting a poster on the MODS optical design at the SPIE meeting in Munich. The text of the paper submitted to the SPIE proceedings is available for download here.

Mechanical Design

Tom has finished redesigning the grating turret with the goal of reducing the overhead above the focal plane. He has succeeded in greatly reducing the amount of overhead, getting back to about 800mm, which was our original working number with earlier designs. This puts the top of the grating mechanism package below the plane of the instrument rotator. He won't push any harder on the design unless told more about what we can or cannot put into that space. Right now we are limited by the grating impinging upon the input beam, and there is not much room left for improvement (of order 10mm or so, much less than the 100's of millimeters we've come down already). The drawings were sent to Jesper Storm at Potsdam, but no report has been received yet. John Hill has also reviewed these drawings and returned comments to Tom. In particular, it looks as if we can widen the instrument package to accommodate the slight stick-out of the Red Camera primary mirror. At least, there is no obvious impediment on the telescope drawings in John's possession. We need to work now with the telescope design people in Italy to make sure this instrument volume is protected. The change we need is to add a "belt" of additional radial volume around the middle of the instrument. Bruce will try to discuss this with personnel in Italy while he is there next week.

Tom is leaving this behind and moving on to other tasks. Among them are working on the multislit mechanism. He has begun addressing the feasibility of our vacuum camera design (see the report for 2000 Feb 16 for background). The deformation of the corrector under vacuum has been computed and the details passed to Paul Byard for analysis in Code-V. Tom is also examining the requirements for a window in front of the CCD for the non-vacuum design. Right now it looks like the window thickness will be 8-10mm for Fused Silica to give us the desired safety margins. Other issues need to be considered and discussions were begun to try to identify which ones we should push on.

R. Pogge, 2000 March 15